Table A1. Trophic position of primary consumers from the four habitat types (Mývatn 200m from shore, Mývatn 5 m from shore, Helluvaðstjrn 200m from shore, Helluvaðstjrn 5 m from shore) and from the two lakes (Mývatn and Helluvaðstjrn):

Herbivore trophic position

Mývatn 5 m from shore

Mývatn 200m from shore

Helluvaðstjrn 5 m from shore

Helluvaðstjrn 200m from shore

Tingidae

2.0

2.0

2.1

2.2

Mývatn

Helluvaðstjrn

Chironomidae

1.9

2.3

Table A2. Absolute and standardized path coefficients for all taxa combined and each family separately.

Taxa

Path

Estimate (absolute)

SE

Estimate (standardized)

P

All combined

(Fig. 3)

δ13C → Trophic position

-0.0100

0.0018

-0.5309

0.0003

δ13C → MeHg

-0.0374

0.0098

-0.3825

0.0007

Trophic position → MeHg

1.9764

0.5210

0.3800

0.0005

Linyphiidae

(Fig. A1A)

δ13C → Trophic position

-0.0132

0.0052

-0.4665

0.0253

δ13C → MeHg

-0.0838

0.0179

-0.7199

0.004

Trophic position → MeHg

0.3048

0.6342

0.0740

0.6287

Lycosidae

(Fig. A1B)

δ13C → Trophic position

-0.0065

0.0024

-0.4926

0.0170

δ13C → MeHg

-0.0521

0.0092

-0.8101

0.0003

Trophic position → MeHg

-0.0845

0.6997

-0.0173

0.9131

Opiliones

(Fig. A1C)

δ13C → Trophic position

-0.0179

0.0028

-0.8730

0.0005

δ13C → MeHg

-0.0609

0.0200

-0.9737

0.0140

Trophic position → MeHg

-0.5255

0.9719

-0.1728

0.6296

Acari

(Fig. A1D)

δ13C → Trophic position

-0.0137

0.0036

-0.6996

0.0045

δ13C → MeHg

-0.0460

0.0167

-0.6458

0.0223

Trophic position → MeHg

0.5619

0.8488

0.1548

0.5230

Table A3. AIC-based model selection. The path structure of the saturated model is as depicted in Fig. 1. The path from trophic position to MeHg is removed in the reduced model.